Copper alloy having bendability and stress relaxation property

ABSTRACT

A copper alloy contains 0.01% to 1.0% of Fe, 0.01% to 0.4% of P, and 0.1% to 1.0% of Mg with the remainder being copper and inevitable impurities and has a volume fraction of dispersoids having a particle diameter exceeding 200 nm of 5% or less, in which dispersoids having a particle diameter of 200 nm or less and containing Mg and P have an average particle diameter of 5 nm or more and 50 nm or less. The copper alloy preferably has an average particle diameter of dispersoids containing Fe and P of 20 nm or less. The copper alloy has improved bendability and stress relaxation property.

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention relates to copper alloyshaving bendability and stress relaxation property. Specifically, itrelates to copper alloys suitable as raw materials for copper alloysheets for use in semiconductor components such as IC lead frames forsemiconductor devices; materials for electric/electronic components suchas printed wiring boards; switch components; and mechanical componentssuch as bus-bars, terminals, and connectors.

2. Description of the Related Art Cu—Fe—P alloys have been generallyused as copper alloys for the above applications such as IC lead framesfor semiconductor devices. Examples of these Cu—Fe—P alloys include acopper alloy (C19210 alloy) containing0.05% to 0.15% of Fe and0.025% to0.040% of P and a copper alloy (CDA194 alloy) containing 2.1% to 2.6% ofFe, 0.015%to 0.15% of P, and0.05% to 0.20% of Zn. Among copper alloys,these Cu—Fe—P alloys exhibit high strength, high electricalconductivity, and high thermal conductivity when an intermetalliccompound of, e.g., Fe or Fe and P, is dispersed in a copper matrix, andtherefore, these have been generally used as the international standardalloys.

With increasing applications, Cu—Fe13 P alloys must have such propertiesas tomaintain contact fitting force inahot environment, i.e., so-calledstress relaxation property, as properties to ensure the reliability in ahot environment. Specifically, when coupling components are placed in ahot environment such as an engine room of an automobile, the stress isrelaxed and contact pressure decreases with elapse of time, and thecontact resistance at a junction tends to increase. Thus, the couplingcomponents lose their contact fitting force. Consequently, the “stressrelaxation property” is resistant properties against the reduction incontact fitting force (stress). It is believed that the stressrelaxation property improves with a decreasing stress relaxation rate.

Various techniques have been proposed in order to improve the stressrelaxation property. Japanese Patent No. 2977839, for example, disclosesa copper alloy for electric/electronic components, containing 0.1 to 1.0percent by weight of Sn, 0.02 to 0.50 percent by weight of Fe, 0.01 to0.1 percent by weight of P, 0.3 to 1.5 percent by weight (excluding1.5percent by weight) of Zn, and 0.1 to 1.0 percent by weight of Mg,with the remainder substantially being Cu. According to this technique,Fe and P are added together to form iron phosphide to thereby improvethe spring limit. In addition, the copper alloy is to have softeningresistance, particularly excellent creep properties at elevatedtemperatures, and stress relaxation property.

Japanese Unexamined Patent Application Publication No. 2002-294368proposes a copper alloy for terminals and connectors, containing 0.8% to1.5% of Ni, 0.5% to 2.0% of Sn, 0.015% to 5.0% of Zn, and 0.005% to 0.1%of P, in which the areal ratio of precipitates is 5% or less to maintainthe resistance of the parent phaseagainststressrelaxation(activityforinhibitingmigration of slipband and dislocationdisappearance) and to improve the stress relaxation property.

The Cu—Fe—P alloys for the above-mentioned applications are required tohave excellent bendability capable of enduring sharp bending such asU-bending or 90° bending after notching, as well as the high strengthand the high electrical conductivity.

However, the above-described addition of solid-solution hardeningelements such as Sn and Mg, or the increase in strength by increasingreduction ratios of the cold rolling inevitably cause deterioration ofthe bendability and, therefore, the required strength and thebendability cannot become mutually compatible.

On the other hand, it is known that the bendability can be improved tosome extent by grain refining or by controlling the state of dispersoids(Japanese Unexamined Patent Application Publication No. 6-235035 andJapanese Unexamined Patent Application Publication No. 2001-279347).However, in order to produce a Cu—Fe—P alloy material having highstrength compatible with reduction in the size and weight of componentsin recent years, an increase in the quantity of work hardening byincreasing reduction ratio of the cold rolling becomes indispensable.

Consequently, as for the above-described high strength materials, thebendability cannot be adequately improved against the above-describedsharp bending such as U-bending or 90° bending after notching, by meansof microstructure control, e.g., grain refining or control of the stateof dispersoids, disclosed in Japanese Unexamined Patent ApplicationPublication No. 6-23503 and Japanese Unexamined Patent ApplicationPublication No. 2001-279347.

As for Cu—Fe—P alloys, Japanese Unexamined Patent ApplicationPublication No. 2002-339028 proposes control of the microstructure.Specifically, it proposes that an intensity ratio, I(200)/I(220), ofdiffraction of (200) to diffraction of (220) is 0.5 or more and 10 orless, the density of Cube orientation is 1 or more and 50 or less, or aratio of the density of Cube orientation to the density of S orientationis 0.1 or more and 5 or less.

Japanese Unexamined Patent Application Publication No. 2000-328157proposes that an intensity ratio, [I(200)+I(311)]/I(220),ofthesumofdiffractionof (200) and diffraction of (311) to diffraction of(220) is 0.4 or more.

SUMMARY OF THE INVENTION

The conventional techniques such as adjusting the alloying component inJapanese Patent No. 2977839 and reducing the areal ratio of precipitatesin Japanese Unexamined Patent Application Publication No. 2002-294368are insufficient to improve the stress relaxation property. Thesetechniques cannot make the alloy to have bendability simultaneously.

The control of the microstructure in Japanese Unexamined PatentApplication Publication No. 2002-339028 and Japanese Unexamined PatentApplication Publication No. 2000-328157 do not achieve the excellentstress relaxation property, although they yield improved bendability.

Accordingly, an object of the present invention is to provide a Cu—Fe—Palloy having excellent bendability compatible with excellent stressrelaxation property.

To achieve the above object, one aspect of the present invention residesin a copper alloy having bendability and stress relaxation property andcontaining 0.01 to 1.0 percent by mass of Fe, 0.01 to 0.4 percent bymass of P, and 0.1 to 1.0 percent by mass of Mg, with the remainderbeing copper and inevitable impurities, in which the copper alloy has avolume fraction of dispersoids each having a particle diameter exceeding200 nm of 5% or less, and dispersoids each having a particle diameter of200 nm or less and containing Mg and P have an average particle diameterof 5 nm or more and 50 nm or less.

To further improve the bendability and the stress relaxation property,dispersoids each having a particle diameter of 200 nm or less andcontaining Fe and P preferably have an average particle diameter of 1 nmor more and 20 nm or less.

The copper alloy can further contain 0.01 to 1.0 percent by mass of atleast one of Ni and Co to further improve the bendability and the stressrelaxation property.

The copper alloy can further contain 0.005 to 3.0 percent by mass of Znfor improving thermal ablation resistance of Sn plating and solder tothereby prevent thermal ablation (heat peeling). The Zn content ispreferably 0.005 to 1.5 percent by mass to avoid reduction in electricalconductivity.

To improve the strength, the copper alloy can further contain 0.01 to5.0 percent by mass of Sn. The Sn content is preferably 0.01 to 1.0percent by mass to avoid reduction in electrical conductivity.

According to the aspect of the present invention, a Cu—Fe—P alloy iscombined with Mg to have improved strength and improved stressrelaxation property and to reduce coarse dispersoids having a particlediameter exceeding 200 nm.

The coarse dispersoids having a particle diameter exceeding 200 nmaccelerate recrystallization in a hot environment to thereby reduce thestress relaxation property, cause breakage in deformation and promotecrack propagation to thereby reduce the bendability.

To further effectively improve the bendability and the stress relaxationproperty by the addition of Mg in the Cu—Fe—P alloy, dispersoidscontaining Mg and P (Mg—P particles) should have an average particlediameter of 5 nm or more and 50 nm or less. These fine Mg—P particlesprevent migration of dislocation and grain growth to thereby highlyeffectively improve the bendability and the stress relaxation property.

Such effects and influence of these fine Mg—P particles on theproperties of Cu—Fe—P alloys have been first found by the presentinventors.

The term “dispersoid containing Mg and P” used herein means a dispersoidcontaining Mg and P in a total content of 60% or more of the totalcomponents in the particle. Likewise, the term “dispersoid containing Feand P” means a dispersoid containing Fe and P in a total content of 60%or more of the total components in the particle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Composition of Copper Alloy

The chemical composition of the Cu—Fe—P alloy of the present inventionsuitable for satisfying the required strength and the electricalconductivity and further satisfying the excellent bendability and theexcellent stress relaxation property will be described below.

In the present invention, as for the basic composition to achieve thehigh strength, high electrical conductivity, high bendability, and highstress relaxation property, the copper alloy comprises 0.01 to 1.0percent by mass of Fe, 0.01 to 0.4 percent by mass of P, and0.1to10percent by mass of Mg, with the remainder being copper and inevitableimpurities.

In another embodiment, the following range of at least one of Ni and Coand/or at least one of Zn and Sn may be further contained relative tothis basic composition. Other impurity elements may be contained withinthe ranges of not impairing these properties.

(Fe)

Iron (Fe) precipitates as Fe or a Fe—P dispersoid having a particlediameter of 200 nm or less, and is an important element which improvesthe strength and the stress relaxation property of the copper alloy. Ifthe contentof Fe is less than 0.01 percent by mass, the quantity ofgeneration of the above-described fine dispersoids is small. The contentof Fe should be 0.01 percent by mass or more to effectively exhibitthese advantages. On the other hand, if the content of Fe exceeds 1.0percent by mass, dispersoids are grown and become coarse, so that thestrength, the bendability, and the stress relaxation property arereduced. Therefore, the content of Fe is specified to be within therange of 0.01 to 1.0 percent by mass.

(P)

Phosphorus (P) effects deoxidation and, in addition, is an importantelement to form fine dispersoids having a particle diameter 200 nm orless with Fe and/or Mg to thereby improve the strength and the stressrelaxation property of the copper alloy. If the content of P is lessthan 0.01 percent by mass, the fine dispersoids are not formedsufficiently. The content of P must be 0.01 percent bymass or more toeffectively exhibit the effects such as the improvement in stressrelaxation property. On the other hand, if the content of P exceeds 0.4percent by mass, dispersoids are grown and become coarse to therebyreduce the bendability, the stress relaxation property, and the hotworkability. Therefore, thecontentof Pisspecifiedtobewithin the range of0.01 to 0.4 percent by mass.

(Mg)

Magnesium (Mg) is an important element to form fine dispersoids having aparticle diameter of 200 nm or less with P in the copper alloy tothereby improve the strength and the stress relaxation property. If thecontent of P is less than 0.1 percent by mass, the fine dispersoids arenot formed sufficiently. The content of Mg must therefore be 0.1 percentby mass or more to effectively exhibit these effects. On the other hand,if the content of Mg exceeds 1.0 percent by mass, dispersoids are grownand become coarse to thereby reduce the strength, the bendability, andthe stress relaxation property. Accordingly, the content of Mg isspecified to be within the range of 0.1 to 1.0 percent by mass.

(Ni, Co)

The copper alloy can further contain 0.01 to 1.0 percent by mass of atleast one of Ni and Co. Nickel (Ni) and cobalt (Co), in commonwith Fe,precipitate as fine dispersoids of, for example, (Ni,Co)—P or(Ni,Co)—Fe—P in the copper alloy to improve the strength and the stressrelaxation property. The total content of Ni and Co must be 0.01 percentby mass or more to effectively exhibit these effects. In contrast, ifthe total content of Ni and Co exceeds 1.0 percent by mass, dispersoidsbecome coarse to thereby reduce the strength, the bendability, and thestress relaxation property. Accordingly, the total content of Ni and Cois specified to be within the range of 0.01 to 1.0 percent by mass.

(Zn)

The copper alloy may further contain at least one of Zn and Sn. Zinc(Zn) is an effective element for improving the thermal ablationresistance and for preventing the thermal ablation of Snplatingandsolder foruse in junction of electronic components. Thecontent of Zn is preferably 0.005 percent by mass or more to effectivelyexhibit these effects. In contrast, an excessively high content of Znreduces the wettability and spreadability of molten Sn and solder and,in addition, significantly reduces the electrical conductivity.Accordingly, Zn is selectively contained at a content of 0.005 to 3.0percent by mass, and preferably 0.005 to 1.5 percent by mass, so as toimprove the thermal ablation resistance and to avoid reduction inelectrical conductivity.

(Sn)

Tin (Sn) is dissolved in the copper alloy and contributes to theimprovement in strength. The content of Sn is preferably 0.01 percent bymass or more to effectively exhibit these effects. On the other hand, ifthe content of Sn is excessively high, the effect thereof is saturated.Conversely, the electrical conductivity is significantly decreased. Inconsideration of this point, Sn is selectively contained at a contentwithin the range of 0.01 to 5.0 percent by mass and preferably 0.01 to1.0 percent by mass.

(Other Elements)

The other elements are basically impurities and are preferablyminimized. For example, impurity elements such as Al, Cr, Ti, Be, V, Nb,Mo, and W may often cause dispersoids to become coarse and induceadecreased electrical conductivity. Accordingly, the total content ofthese elements is preferably minimized to 0.5 percentbymassorless.Otherminorelementsinthecopperalloy, such as B, C, Na, S, Ca, As, Se, Cd,In, Sb, Pb, Bi, and MM (misch metals), maycauseadecreasedelectricalconductivity. The total content of these elements is thereforepreferably minimized to 0.1 percent by mass or less.

More specifically, it is preferred that (1) the total content of Mn, Ca,Zr, Ag, Cr, Cd, Be, Ti, Co, Ni, Au, and Pt is 1.0 percent by mass orless, and that (2) the total content of Hf, Th, Li, Na, K, Sr, Pd, W, S,Si, C, Nb, Al, V, Y, Mo, Pb, In, Ga, Ge, As, Sb, Bi, Te, B, and mischmetals is 0.1 percent by mass or less.

(Dispersoid Distribution)

Next, the distribution of dispersoids in the copper alloy is specifiedas follows so to achieve the high stress relaxation property and thehigh bendability.

(Coarse Dispersoids)

The coarse dispersoids having a particle diameter exceeding 200 nm inthe copper alloy accelerate recrystallization in a hot environment tothereby reduce the stress relaxation property, cause breakage indeformation and promote crack propagation to thereby reduce thebendability, regardless of the composition thereof. Consequently, thevolume fraction of coarse dispersoids having a particle diameterexceeding 200 nm in the copper alloy should be minimized to 5 percent bymass or less, regardless of the composition of the dispersoids.

(Mg-P Particles)

Of dispersoids having a particle diameter of 200 nm or less, thosecontaining Mg and P (Mg—P particles) are specified to have an averageparticle diameter of 5 nm or more and 50 nm or less. These fine Mg—Pparticles highly contribute to inhibiting the dislocation migration andthe grain growth and to the improvement in bendability and stressrelaxation property.

According to the present invention, Mg—P particles having a particlediameter exceeding 200 nm are minimized and Mg—P particles having aparticle diameter of 200 nm or less are specified to have theabove-specified average particle diameter. The Mg—P particles having aparticle diameter exceeding 200 nm are excluded from the calculation ofthe average particle diameter. This is because Mg—P particles having aparticle diameter exceeding 200 nm should be minimized, and fine Mg—Pparticles highly contributing to the improvement in bendability andstress relaxation property should be increased.

If the average particle diameter of dispersoids having a particlediameter of 200 nm or less and containing Mg and P exceeds 50 nm, thedislocation migration and the grain growth are not effectivelyinhibited. Consequently, the upper limit of the average particlediameter of the dispersoids mainly containing Mg and P is specified tobe 50 nm. In contrast, if the average particle diameter of thedispersoids containing Mg and P is less than 5 nm, the particles do noteffectively contribute to the inhibition of the dislocation migrationand the grain growth and fail to improve the stressrelaxationpropertyandthebendability. Accordingly, the lower limit of theaverage particle diameter of the dispersoids mainly containing Mg and Pis specified to be 5 nm.

(Fe—P Particles)

Of dispersoids having a particle diameter of 200 nm or less, dispersoidsmainly containing Fe and P (Fe—P particles) having an average particlediameter of 1 to 20 nm exhibit significantly higher pinning force toinhibit the migration and disappearance of dislocation than coarsedispersoids. Accordingly, the average particle diameter of dispersoidshaving a particle diameter of 200 nm or less and containing Fe and P ispreferably within the range of 1 nm or more and 20 nm or less, forfurther improving the bendability and the stress relaxation property.

When the copper alloy further comprises at least one of Ni and Co, theseelements form dispersoids containing Ni and/or Co, such as (Ni, Co)—Pand (Ni, Co)—Fe—P particles in the copper alloy. The dispersoidscontaining Ni and/or Co preferably have an average particle diameter of1 nm or more and 20 nm or less for further improving the bendability andthe stress relaxation property, as in the Fe—P particles.

However, Ni/Co dispersoids containing Fe, such as (Ni,Co) —Fe—Pparticles, are substantially included in the “Fe—P particles” as usedherein. If dispersoids containing Ni and/or Co other than the Fe—Pparticles, such as (Ni,Co)—P particles, are present, they can be refinedas a result of refining of the Fe—P particles typically by theafter-mentioned preferred production method. Accordingly, even when thecopper alloy further comprises at least one of Ni and Co, thedispersoids containing Ni and/or Co are not specified and determined,and the Fe—P particles are specified as representative.

In the present invention, Fe—P particles having a particle diameterexceeding 200 nm are minimized, and the average particle diameter of theFe-P particles having a particle diameter of 200 nm or less is specifiedwithin the above range. Fe—P particles having a particle diameterexceeding 200 nm are excluded from the calculation of the averageparticle diameter. This is because fine Fe—P particles highlycontributing to the improvement in bendability and stress relaxationproperty should preferably be increased, as in the Mg—P particles.

If the average particle diameter of the dispersoids mainly containing Feand P exceeds 20 nm, the pinning force decreases. Accordingly, thepreferred upper limit of the average particle diameter of thedispersoids mainly containing Fe and P is 20 nm.

In contrast, if the average particle diameter of the dispersoids mainlycontaining Fe and P is less than 1 nm, such particles cannot be detectedand determined even using a transmission electron microscope at amagnification of 100,000 times and may have a low pinning force.Consequently, the preferred lower limit of the average particle diameterof the dispersoids mainly containing Fe and P is 1 nm.

These fine Mg—P particles and fine Fe—P particles (dispersoids) areformed, for example, in annealing after cold rolling in the productionof the copper alloy. Specifically, these fine dispersoids are compoundphases finely precipitated from the parent phase as a result ofannealing.

The fine dispersoids are thereby different from coarse dispersoidsformed upon casting and present in the copper alloy. Such finedispersoids in the copper alloy can only be observed, for example, witha transmission electron microscope at a magnification of 100,000 ormore.

In other words, these dispersoids containing Fe and P and having anaverage particle diameter of 1 nm or more and 20 nm or less anddispersoids containing Mg and P and having an average particle diameterof 5 nm or more and 50 nm or less can be identified by the observationof the copper alloy with a transmission electron microscope at amagnification of 100,000. This observation enables distinction betweenMg—P particles each containing Mg and P in a total content of 60% ormore of the total components and the other particles, distinctionbetween Fe—P particles containing Fe and P in a total content of 60% ormore of the total components and the other particles, and identificationof dispersoids containing Ni and/or Co.

The average particle diameters of the Mg—P particles and the Fe—Pparticles each having a particle diameter of 200 nm or less aredetermined in the following manner by observing the microstructure witha transmission electron microscope (TEM) at a magnification of 100,000.Initially, the largest diameter of each dispersoid in the microstructurein a visual field 1 pm long 1 μm wide (1 μm²) of TEM is measured as theparticle diameter d of each dispersoid.

Next, the total areal ratio of all these dispersoids having a particlediameter d exceeding 200 nm is determined. The total areal ratio isdefined as the volume fraction of dispersoids each having a particlediameter exceeding 200 nm in the present invention.

The Fe—P particles having a total content of Fe and P of 60% or more andthe Mg—P particles having a total content of Mg and P of 60% or more aredistinguished based on the total content of Fe and P, and the totalcontent of Mg and P, respectively, in the following manner. Asemiquantitative analysis by energy dispersive X-ray spectroscopy (EDX)using electron prove X-ray microanalysis (EPMA) is used herein. Thistechnique is generally used for analyzing microstructures. Thus, thetotal content of Mg and P, and the total content of Fe and P in eachdispersoid are determined. Particles containing 60% or more of Fe and P,and those containing 60% or more of Mg and P are identified as the Fe—Pparticles and the Mg—P particles, respectively.

The largest diameter of each of the Fe—P particles or Mg—P particleseach having the particle diameter d of 200 nm or less is determined. Thelargest diameters are then averaged. Thus, the average particle diameterof the Fe—P particles or Mg—P particles each having a particle diameterof 200 nm or less is determined.

(Production Condition)

Preferable production conditions to make the copper alloy compatiblewith the above-described microstructure specified according to thepresent invention will be described below. The copper alloy of thepresent invention is basically a copper alloy sheet, and a stripprepared by cutting the sheet in a widthwise direction and a coil madefrom the sheet or strip are also included in the copper alloy of thepresent invention. The copper alloy of the present invention can beproduced through the same process as the normal process, except forpreferable conditions in the cold rolling and the annealing to attainthe above-described microstructure specified according to the presentinvention. Therefore, the normal production process itself is in no needof being changed significantly.

That is, a copper alloy melt adjusted to have the above-describedpreferable chemical composition is cast. The resulting ingot issubjected to facing, and to heating or a homogenizing heat treatment.Thereafter, hot rolling is performed.

Water-quenching is preferably performed after the completion of hotrolling to prevent formation of coarse dispersoids having a particlediameter exceeding200 nm at elevated temperatures.

Subsequently, cold rolling and annealing are performed to yield a copperalloy sheet having a desired thickness as the product.

For controlling the dispersion of the Mg—P particles and theFe-Pparticles within the ranges specified in thepresent invention, it iseffective to perform the annealing under the following conditions. Thefine dispersoids herein are compound phases newly precipitated from theparent phase as a result of annealing. To precipitate these finedispersoids, annealing is performed subsequent to cold rolling after hotrolling in the production of the copper alloy.

However, if the precipitation of dispersoids is to be increased by onlyone pass of annealing, the annealing temperature must be elevated, andsuch a high annealing temperature causes dispersoids to grow and to becoarse. Thus, the Mg—P particles and the Fe—P particles may have anexcessively large average particle diameter exceeding theabove-specified ranges.

Consequently, it is preferred to perform plural annealing passes whilecontrolling the annealing temperature in each process to 430° C. orlower. Thus, the desired precipitation of dispersoids is obtained, andthe growth of the dispersoids is prevented to thereby yield the finedispersoids. If the annealing time (holding time) is excessively long,the dispersoids may grow and become coarse. Thus, an optimal annealingtime is preferably set.

In addition, cold rolling is preferably performed between theseannealing passes. The cold rolling increases lattice defects which serveas precipitation nuclei in the subsequent annealing and contribute tothe formation of the fine dispersoids.

In consideration of these conditions, it is preferred to perform twocold rolling processes and two annealing processes between hot rollingand finish cold rolling in the production of the copper alloy so as toyield the fine dispersoids having the above configuration.

EXAMPLES

The present invention will be illustrated in further detail withreference to several experimental examples below. Specifically, a seriesof thin copper alloy sheets was producedbyaprocesscomprisingeachtwopassesofcoldrollingandannealing (hotrolling-cold rolling-primary annealing-cold rolling-secondaryannealing-finish cold rolling) at a varying composition under varyingannealing conditions (temperature and time). Properties such as thehardness, the electrical conductivity, and the bendability of thesecopper alloy sheets were evaluated.

Specifically, each copper alloy having the chemical composition shown inTable 1 was melted in a coreless furnace, and an ingot-making wasperformed by a semicontinuous casting method to yield an ingot 70 mmthick, 200 mm wide, and 500 mm long. The surface of each ingot wassubjected to facing, followed by heating. Thereafter, hot rolling wasperformed to prepare a sheet 16 mm thick, and the resulting sheet wasquenched in water from a temperature of 650° C. or higher. Oxidizedscale was removed and, thereafter, primary cold rolling (intermediaterolling) was performed. The resulting sheet was subjected to facing and,thereafter, to primary annealing and cold rolling. Subsequently,secondary annealing and finish cold rolling were performed, and thenstrain relieving annealing at a low temperature was performed to therebyyield a copper alloy sheet about 0.2 mm thick.

In each copper alloy shown in Table 1, the remainder of the compositionother than the elements described in Table 1 was Cu. The total contentof other elements, i.e., Al, Cr, Ti, Be, V, Nb, Mo, and W was 0.1percent by mass or less. The total content of impurity elements such asB, C, Na, S, Ca, As, Se, Cd, In, Sb, Pb, Bi, and MM (misch metals) wasalso 0.1 percent by mass or less.

The temperature and the time (° C.×hr)of each pass of annealing areshown in Table 1.

In each example, samples were cut from the thus produced copper alloysheet, and the volume fraction (%) of dispersoids each having a particlediameter exceeding200 nm, the average particle diameter (nm) ofdispersoids having a particle diameter of 200 nm or less and containingMg and P, and the average particle diameter (nm) of dispersoids having aparticle diameter of 200 nm or less and containing Fe and P in themicrostructure were determined by the above methods. The results areshown in Table 2.

Separately, samples were cut from the thus produced copper alloy sheet,the hardness and the electrical conductivity were measured, and abending test and a stress relaxation property test were performed. Theresults are also shown in Table 2.

(Measurement of Hardness)

A measurement of hardness of the copper alloy sheet sample was performedat four points with a micro Vickers hardness meter by applying a load of0.5 kg, and an average value thereof was taken as the hardness.

(Measurement of Electrical Conductivity)

The copper alloy sheet sample was processed into a slip-shaped testpiece of 10 mm in width and 300 mm in length by milling, an electricresistance was measured with a double bridge resistance meter, andtheelectrical conductivitywas calculatedby an average cross-sectional areamethod.

(Evaluation of Bendability)

A bending test of the copper alloy sheet sample was performed inconformity with Japan Copper and Brass Association Standard. A testpiece of 10 mm in width and 30 mm in length was taken from each sample,Good Way bending (the bending axis is perpendicular to the rollingdirection) was performed, and the presence or absence of cracking at thebending portion was visually observed under an optical microscope at amagnification of 50 times. The bendability was evaluated according tothe following criteria: Good: no cracking, Fair: slight cracking,Failure: apparent cracking.

(Stress-Relaxation Resistance)

Each test piece was heated and held at 150° C. for 1,000 hours and thestress relaxation property of the test piece was evaluated according tothe method of Electronics Materials Manufacturers Association of JapanStandard (EMAS-3003). Specifically, one side of the test piece afterheating was held, and the stress under a load of 80% of the 0.2% proofstress as an initial stress was determined. The stress relaxation ratio(%) was determined according to the following equation: Stressrelaxation ratio (%)={[(Stress of the test piece after heating)−(Stressof the test piece before heating)]/(Stress of the test piecebeforeheating)}×100. This test is performed to determine the change in stresstypically of a terminal when held at high temperatures under a constantstrain for a long time. An alloy having a lower relaxation ratio isevaluated a shaving a higher stress relaxation resistance. The stressrelaxation property in parallel with the rolling direction wasevaluated.

Table 1 shows that Inventive Samples 1 to 13 are copper alloys havingcompositions satisfying the requirements in the present invention andhave been produced under preferred conditions in which each two passesof cold rolling and annealing are conducted and the annealingtemperature in each pass is set at 430° C. or lower.

Inventive Samples 1 to 13 have a volume fraction of dispersoids eachhaving a particle diameter exceeding 200 nm of 5% or less, in whichdispersoids containing Mg and P have an average particle diameter of5nmor more and 50 nm or less, and dispersoids containing Fe and P have anaverage particle diameter of 1 nm or more and 20 nm or less. The lastparameter herein is a preferred requirement.

Consequently, Inventive Samples 1 to 13 have a high strength and a highelectrical conductivity of a proof stress of 400 MPa or more, a hardnessof 135 Hv or more, and an electrical conductivity of 60% IACS or moreand are excellent in bendability and stress relaxation property.

In contrast, the copper alloy of Comparative Sample 14 has an Fe contentlower than the lower limit of 0.01 percent by mass. This copper alloyhas Mg and P contents satisfying the requirements in the presentinvention and has been produced under preferred conditions including theannealing temperatures. Thus, it has an average particle diameter ofdispersoids containing Mg and P satisfying the requirement in thepresent invention, thereby has excellent bendability and stressrelaxation property, but has a low strength. It fails to achieve a highstrength and a high electrical conductivity.

The copper alloy of Comparative Sample 15 has an Fe content higher thanthe upper limit of 1.0 percent by mass. This copper alloy has Mg and Pcontents satisfying the requirements in the present invention and hasbeen produced under preferred conditions including the annealingtemperatures. Thus, it has an average particle diameter of dispersoidscontaining Mg and P satisfying the requirement in the present invention,but has a volume fraction of dispersoids having a particle diameterexceeding 200 nm exceeding 5% and thereby shows not only a low strengthbut also a low bendability and a low stress relaxation property.

The copper alloy of Comparative Sample 16 has a P content lower than thelower limit of 0.01 percent by mass. This copper alloy has been producedunder preferred conditions including the annealing temperatures andthereby has an average particle diameter of dispersoids containing Mgand P satisfying the requirement in the present invention. However, ithas a low stress relaxation property, since the insufficient P contentinvites an insufficient absolute quantity of fine dispersoids containingMg and P.

The copper alloy of Comparative Sample 17 has a P content higher thanthe upper limit of 0.4 percent by mass. Although the alloy has beenproduced under preferred conditions including the annealingtemperatures, it contains coarse dispersoids containing Mg and P havingan average particle diameter exceeding the upper limit. In addition, thealloy has a markedly low electrical conductivity because of excessive Pdissolved to form a solid solution and is low in strength, bendability,and stress relaxation property.

The copper alloy of Comparative Sample 18 has a Mg content lower thanthe lower limit of 0.1 percent by mass. This copper alloy has beenproduced under preferred conditions including the annealing temperaturesand thereby has an average particle diameter of dispersoids containingMg and P satisfying the requirement in the present invention. However,it has a low bendability and a low stress relaxation property because ofthe insufficient absolute quantity of fine dispersoids containing Mg andP.

The copper alloy of Comparative Sample 19 has a Mg content higher thanthe upper limit of 1.0 percent by mass. Although the alloy has beenproduced under preferred conditions including the annealingtemperatures, it contains coarse dispersoids containing Mg and P havingan average particle diameter exceeding the upper limit, has a volumefraction of dispersoids having a particle diameter exceeding 200 nmexceeding 5%, and thereby is low in strength, bendability, and stressrelaxation property.

The copper alloy of Comparative Sample 20 has a composition within therange specified in the present invention, but it has been subjected toprimary annealing at an excessively high annealing temperature exceeding430° C., although the secondary annealing temperature is lower than 430°C. The resulting copper alloy contains coarse dispersoids containing Mgand P and coarse dispersoids containing Fe and P each having an averageparticle diameter higher than the upper limit and has a volume fractionof dispersoids having a particle diameter exceeding 200 nm exceeding 5%.Consequently, it has a low strength, a low bendability, and a low stressrelaxation property.

The copper alloy of Comparative Sample 21 has a composition within therange specified in the present invention, but it has been subjected toprimary annealing for an excessively long time, although the temperaturetherein is lower than 430° C. The resulting copper alloy contains coarsedispersoids containing Mg and P and coarse dispersoids containing Fe andP each having an average particle diameter higher than the upper limitand has a volume fraction of dispersoids having a particle diameterexceeding200 nm exceeding 5%. Consequently, it has a low strength, a lowbendability, and a low stress relaxation property.

The copper alloy of Comparative Sample 22 has a composition within therange specified in the present invention, but it has been subjected toprimary annealing at an excessively low temperature. The copper alloy isthereby low not only in electrical conductivity but also in bendabilityand stress relaxation property due to insufficient absolute quantitiesof fine dispersoids containing Mg and P and fine dispersoids containingFe and P.

The copper alloy of Comparative Sample 23 has a composition within therange specified in the present invention, but it has been subjected tosecondary annealing at an excessively high annealing temperatureexceeding 430° C., although the primary annealing temperature is lowerthan 430° C. The resulting copper alloy contains coarse dispersoidscontaining Mg and P and coarse dispersoids containing Fe and P eachhaving an average particle diameter higher than the upper limit and hasa volume fraction of dispersoids having a particle diameter exceeding200 nm exceeding 5%. Consequently, it has a low strength, a lowbendability, and a low stress relaxation property.

The copper alloy of Comparative Sample 24 has a composition within therange specified in the present invention, but it has been subjected tosecondary annealing for an excessively long time, although thetemperature therein is lower than 430° C. The resulting copper alloycontains coarse dispersoids containing Mg and P and coarse dispersoidscontaining Fe and P each having an average particle diameter higher thanthe upper limit and has a volume fraction of dispersoids having aparticle diameter exceeding 200 nm exceeding 5%. Consequently, it hasalow strength, a low bendability, and a low stress relaxation property.

The copper alloy of Comparative Sample 25 has a composition within therange specified in the present invention, but it has been subjected tosecondary annealing at an excessively low temperature. The copper alloyis thereby low not only in electrical conductivity but also inbendability and stress relaxation property due to insufficient absolutequantities of fine dispersoids containing Mg and P and fine dispersoidscontaining Fe and P.

When each one pass of cold rolling and annealing is carried out and theannealing temperature is higher than 430° C., the annealing time isexcessively long, or the annealing temperature is excessively low, theresults are similar to those in Comparative Samples 20 to 025.

These results corroborate the significance of the critical compositionand dispersoids of the copper alloy of the present invention to achievehigh strength and high electrical conductivity, as well as excellentbendability and excellent stress relaxation property, and thesignificance of preferable production conditions to attain therequirements in dispersoids. TABLE 1 Primary Secondary Chemicalcomposition of copper alloy sheet (remainder: Cu and impurities)annealing annealing Case Alloy No. Fe P Mg Ni Co Zn Sn (° C. × hr) (° C.× hr) Inventive 1 0.15 0.10 0.25 — — — — 380 × 5 380 × 5 Sample 2 0.020.10 0.25 — — — — 380 × 5 380 × 5 3 0.91 0.10 0.25 — — — — 380 × 5 380 ×5 4 0.15 0.02 0.25 — — — — 380 × 5 380 × 5 5 0.15 0.36 0.25 — — — — 380× 5 380 × 5 6 0.15 0.10 0.10 — — — — 380 × 5 380 × 5 7 0.15 0.10 0.92 —— — — 380 × 5 380 × 5 8 0.15 0.10 0.25 — — 0.4  — 380 × 5 380 × 5 9 0.150.10 0.25 — — — 0.4  380 × 5 380 × 5 10 0.15 0.10 0.25 — — 0.10 0.10 380× 5 380 × 5 11 0.15 0.10 0.25 0.20 — — — 380 × 5 380 × 5 12 0.15 0.100.25 — 0.20 — — 380 × 5 380 × 5 13 0.10 0.10 0.25 0.20 0.20 0.10 0.10380 × 5 380 × 5 Comparative 14 0.004 0.10 0.25 — — — — 380 × 5 380 × 5Sample 15 1.05 0.10 0.25 — — — — 380 × 5 380 × 5 16 0.15 0.004 0.25 — —— — 380 × 5 380 × 5 17 0.15 0.46 0.25 — — — — 380 × 5 380 × 5 18 0.150.10 0.04 — — — — 380 × 5 380 × 5 19 0.15 0.10 1.1 — — — — 380 × 5 380 ×5 20 0.10 0.10 0.25 0.20 0.20 0.10 0.10 450 × 5 380 × 5 21 0.10 0.100.25 0.20 0.20 0.10 0.10 380 × 30 380 × 5 22 0.10 0.10 0.25 0.20 0.200.10 0.10 250 × 5 380 × 5 23 0.10 0.10 0.25 0.20 0.20 0.10 0.10 380 × 5450 × 5 24 0.10 0.10 0.25 0.20 0.20 0.10 0.10 380 × 5 380 × 30 25 0.100.10 0.25 0.20 0.20 0.10 0.10 380 × 5 250 × 5

TABLE 2 Copper alloy sheet microstructure Volume fraction of Copperalloy sheet properties dispersoids having a Average particle Averageparticle Proof Electrical Stress particle diameter diameter of Mg—Pdiameter of Fe—P stress Hardness conductivity Bend- relaxation CaseAlloy No. exceeding 200 nm (%) dispersoids (nm) dispersoids (nm) (MPa)(Hv) (% IACS) ability rate (%) Inventive 1 2.1 30 10 410 136 71.0 Good16 Sample 2 1.3 38 6 403 135 68.7 Good 16 3 4.3 27 25 415 137 65.5 Good19 4 1.9 30 15 408 136 68.0 Good 15 5 2.5 35 23 417 137 63.8 Good 19 61.5 18 10 405 135 69.0 Good 17 7 3.9 42 12 428 140 63.5 Good 15 8 2.1 3110 433 141 62.1 Good 16 9 1.8 26 8 440 143 61.0 Good 14 10 2.0 28 9 432141 63.0 Good 15 11 2.3 30 11 425 139 67.5 Good 15 12 2.0 29 10 427 14067.7 Good 16 13 1.9 27 9 431 141 63.4 Good 15 Comparative 14 1.1 40 5360 126 65.0 Good 17 Sample 15 5.2 30 28 418 137 64.3 Failure 23 16 1.729 15 395 133 67.5 Good 22 17 3.0 58 25 406 136 59.0 Failure 23 18 1.318 12 400 134 68.4 Fair 22 19 5.5 61 14 430 140 61.8 Failure 21 20 5.355 24 392 133 63.5 Failure 24 21 5.2 54 23 390 132 63.3 Failure 24 222.0 26 8 421 138 57.8 Fair 22 23 5.4 55 25 390 132 63.8 Failure 25 245.2 55 25 387 131 63.5 Failure 25 25 1.9 26 8 420 138 58.0 Fair 22

Table 3 shows another experimental example in which copper alloys haveamounts of the selectively added elements and/or the other elements(impurities) exceeding the preferred upper limits. These samples arethin copper alloy sheets 0.2 mm thick produced under the same conditionsas in the above experimental example (the conditions for the inventivesamples). The properties, such as hardness, electrical conductivity, andbendability, of these thin copper alloy sheets were determined by theprocedure of the above experimental example. The results are shown inTable 4.

Inventive Sample 26 in Table 3 corresponds to Inventive Sample 1 of theabove experimental example in Tables 1 and 2, in which the contents ofthe other elements (impurity elements) are further specified.

Inventive Sample 27 has a high total content of the elements of Group Ain Table 3, i.e., Mn, Ca, Zr, Ag, Cr, Cd, Be, Ti, Co, Ni, Au, and Pt.

Inventive Sample 28 has a high total content of the elements of Group Bin Table 3, i.e., Hf, Th, Li, Na, K, Sr, Pd, W, S, Si, C, Nb, Al, V, Y,Mo, Pb, In, Ga, Ge, As, Sb, Bi, Te, B, and misch metals, exceeding 0.1percent by mass.

Inventive Samples 29 and 30 each have a high Zn content. InventiveSamples 31 and 32 each have a high Sn content.

These Inventive Samples 27 to 32 have contents of principal elements ofFe, P, and Mg within the specified ranges in the present invention andhave been produced under the preferred conditions. These copper alloyssatisfy the requirements on dispersoids in the present invention andhave a high proof stress, a high hardness, an excellent bendability, andan excellent stress relaxation property. They, however, have a lowerelectrical conductivity than Inventive Sample 26 (corresponding toInventive Sample 1 in Tables 1 and 2), due to high contents of the otherelements.

Comparative Samples 33 and 34 have Zn and Sn contents higher than thepreferred upper limits. These copper alloys have contents of principalelements of Fe, P, and Mg within the specified ranges in the presentinvention and have been produced under the preferred conditions, satisfythe requirements on dispersoids in the present invention and have a highproof stress, a high hardness, an excellent bendability, and anexcellent stress relaxation property. However, they have a markedlylower electrical conductivity than Inventive Samples Sample 27 to 32,due to high Zn and Sn contents. TABLE 3 Chemical composition of copperalloy sheet (remainder: Cu) Primary Secondary Total content Totalcontent annealing annealing Case Alloy No. Fe P Mg Ni Co Zn Sn of GroupA of Group B (° C. × hr) (° C. × hr) Inventive 26 0.15 0.10 0.25 — — — —0.05 0.02 380 × 5 380 × 5 Sample 27 0.15 0.10 0.25 — — — — 0.55 0.02 380× 5 380 × 5 28 0.15 0.10 0.25 — — — — 0.12 0.12 380 × 5 380 × 5 29 0.150.10 0.25 — — 1.6 — 0.12 0.02 380 × 5 380 × 5 30 0.15 0.10 0.25 — — 2.5— 0.12 0.02 380 × 5 380 × 5 31 0.15 0.10 0.25 — — — 1.5 0.12 0.02 380 ×5 380 × 5 32 0.15 0.10 0.25 — — — 4.0 0.12 0.02 380 × 5 380 × 5Comparative 33 0.15 0.10 0.25 — — 3.5 — 0.12 0.02 380 × 5 380 × 5 Sample34 0.15 0.10 0.25 — — — 5.5 0.12 0.02 380 × 5 380 × 5Group A: Mn, Ca, Zr, Ag, Cr, Cd, Be, Ti, Co, Ni, Au, and PtGroup B: Hf, Th, Li, Na, K, Sr, Pd, W, S, Si, C, Nb, Al, V, Y, Mo, Pb,In, Ga, Ge, As, Sb, Bi, Te, B, and misch metal

TABLE 4 Copper alloy sheet microstructure Volume fraction of Copperalloy sheet properties dispersoids having a Average particle Averageparticle Proof Electrical Stress particle diameter diameter of Mg—Pdiameter of Fe—P stress Hardness conductivity Bend- relaxation CaseAlloy No. exceeding 200 nm (%) dispersoids (nm) dispersoids (nm) (MPa)(Hv) (% IACS) ability rate (%) Inventive 26 2.1 30 10 410 136 71.0 Good16 Sample 27 3.0 33 12 415 137 61.5 Good 19 28 2.5 32 11 412 136 63.3Good 18 29 2.1 30 11 445 144 60.4 Good 16 30 2.1 31 10 454 146 58.8 Good15 31 1.8 25 8 450 145 59.3 Good 14 32 1.7 24 7 472 150 56.2 Good 13Comparative 33 2.1 31 10 459 147 54.7 Good 15 Sample 34 1.7 24 7 479 15252.4 Good 13

As is described above, according to the present invention, the Cu-Fe-Palloy which has excellent bendability and excellent stress relaxationproperty can be provided without loss of the high strength and the highelectrical conductivity. Consequently,theresultingcopperalloycanbeappliedtoleadframes, connectors, terminals,switches, relays, and other uses, in addition to IC lead frames forsemiconductor devices, to serve as a downsized and lightweight electricand electronic component, in which high strength, high electricalconductivity, excellent bendability capable of enduring sharp bendingand excellent stress relaxation property are required.

While the present invention has been disclosed in terms of the preferredembodiment in order to facilitate better understanding thereof, itshouldbe appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodification to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

1. A copper alloy having bendability and stress relaxation property andcomprising 0.01 to 1.0 percent by mass of Fe, 0.01 to 0.4 percent bymass of P, and 0.1 to 1.0 percent by mass of Mg, with the remainderbeing copper and inevitable impurities, wherein the copper alloy has avolume fraction of dispersoids each having a particle diameter exceeding200 nm of 5% or less, and wherein dispersoids each having a particlediameter of 200 nm or less and containing Mg and P have an averageparticle diameter of 5 nm or more and 50 nm or less.
 2. The copper alloyaccording to Claim 1, wherein dispersoids each having a particlediameter of 200 nm or less and containing Fe and P have an averageparticle diameter of 1 nm or more and 20 nm or less.
 3. The copperalloyaccording to one of claims 1 and 2, further comprising 0.01 to 1.0percent by mass of at least one of Ni and Co.
 4. The copper alloyaccording to any one of claims 1 to 3, further comprising 0.005 to 3.0percent by mass of Zn.
 5. The copper alloy according to any one ofclaims 1 to 4, further comprising 0.01 to 5.0 percent by mass of Sn. 6.The copper alloy according to any one of claims 1 to 5, wherein thecopper alloy has a total content of Mn, Ca, Zr, Ag, Cr, Cd, Be, Ti, Co,Ni, Au, and Pt of 1.0 percent by mass or less.
 7. The copper alloyaccording to any one of claims 1 to 6, wherein the copper alloy has atotal content of Hf, Th, Li, Na, K, Sr, Pd, W, S, Si, C, Nb, Al, V, Y,Mo, Pb, In, Ga, Ge, As, Sb, Bi, Te, B, and misch metals of 0.1 percentby mass or less.